Film-Tech Forum ARCHIVE: Can you check a diode without removing it?

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Posted by Frank Dubrois (Member # 3042) on 07-13-2006, 03:52 PM:

I was just curious if it was possible to get any kind of reliable reading while checking diodes without actually taking them out first? We have a Christie P35GP with 6 diodes. When these things go out, 99% of the time taken to replace the bad diode is used removing perfectly good diodes to check them, then replacing them and moving on to the next one. I am not aware of a proceedure to get an accurate reading without removing the diode first, but was wondering if anyone else did? We'd really love to be able to find the bad diode and replace it, and get the show going again. A blown diode usually means a blown show and passes, but a quick repair would not only make customers happy, but save us a lot of work. Thanks

Posted by Aaron Sisemore (Member # 145) on 07-13-2006, 05:57 PM:

Yes, as long as you completely disconnect one (or both, in some cases) ends of the diode from the circuit, and leave them bolted into the heat sink.

-Aaron

Posted by Michael Schaffer (Member # 1204) on 07-13-2006, 07:59 PM:

You can't accurately measure it without disconnecting one end, as Mr Sisemore pointed out, but one way to speed up the process to find the bad diode is to use a contactless laser thermometer and/or a current clamp. If a diode is shorted, it will get much hotter than the other diode as it conducts way more current. Although that often trips the breaker quickly, so there isn't much time for it to heat up. But you can often see the difference in temperature. An open diode will be colder. Or you can check the cables going from the mainboard into the diode heatsink with a clamp-on ampmeter. It will quickly tell you which diode is conducting excessive, which is conducting no current.

Posted by Mark Gulbrandsen (Member # 72) on 07-13-2006, 08:25 PM:

Oh come on guys... If you're doing your job corectly you will simply replace all of the diodes and you will be both time and money ahead of any repeat failures of the others you didn't replace. Even a semi-experienced tech can replace them all in about 30 minutes. Repeat failures of the ones you left in there usually happens shortly down the road or at the next power bump. Diodes have a finite life and they tend to mechanically break down from the repeated thermal expansion and contraction they constantly undergo. An entire set of diodes is alot cheaper than refunding a house with just 30 people in it. Also get the latest diodes. The IR diodes that Christie uses are not all that great. I use Semikron diodes rated at nearly double the current of the Christie diodes and they are in the same size case. They are much less expensive once you know where to get them and far more reliable than the IR originals that came in your rectifier.

Mark

Posted by Charles Greenlee (Member # 3856) on 07-13-2006, 08:57 PM:

Good point Mark. It's kind of like a fouled spark plug in a car. You don't just replace the one beause you know the others aren't 100% even if they haven't yet failed, and its not that much more work, and its cheap enough simply to avoid another breakdown in another few weeks. At the Wynnsong, ours sat in a block (pack), you can't remove them one at a time. You pull the whole block. And one of the few things we did right there is we had a spare block. Remove the old, put in the new, and you're back running. Then you take the old block to your service bench and do the replacing there taking your time to do it right, because the projector's running with the new pack. If you still feel the need to do testing and replace just the bad ones, you'd do it then, since you have time.

I'd say replacing just the bad one is only for an emergency situation (sold out premere of Star Wars Ep. 7: the return of Darth Plattrus), and only if you can tell by sight (scorched), because it probably won't save you any time, and may cost you more.

Posted by Christopher Seo (Member # 7) on 07-13-2006, 09:59 PM:

If one has a desire to get electrocuted, couldn't one read the voltage drop across the diodes while the rectifier is on?

Posted by Charles Greenlee (Member # 3856) on 07-13-2006, 10:19 PM:

Standard voltage drop is either .7 or .3 V. Projector diodes I'm not sure about. But if you're getting a very high drop, would indicate an open circuit, and a low to nonexistant drop would indicate an internal short. But I wouldn't be messing with anything that powerful hot. Best just cut power and remove the whole pack and replace. Besides, even if you found the bad one without electrocuting yourself, then what? You'd still have to power down, remove the diode, or pack, and replace. Might as well just do them all while you're in there.

Posted by Frank Dubrois (Member # 3042) on 07-13-2006, 10:31 PM:

I agree with replacing them all, but my goal is to get a bad diode changed out as soon as possible to get the show going. Even if we have to hand out passes...at least the customers didnt have to wait for the show to continue. I dont know how comfortable I am poking around inside there with the power on...I might have to continue doing it the slow way.

Posted by Charles Greenlee (Member # 3856) on 07-13-2006, 10:49 PM:

Yeah, better safe than dead I always say.

Posted by Mark Gulbrandsen (Member # 72) on 07-13-2006, 10:49 PM:

Frank,
I think you missed the point completely. You can change them all out faster than you can find the bad one. It still involves disconnecting one end of each diode anyway and with the correct tools its a breeze. Have a tube of GC Silicone heatsink grease at hand when you do it.

Absolutely DO NOT work on a live rectifier. Even the expereinced have been electrocuted this way. Some rectifiers are pretty tight with a lack of space inside and sharp corners and metal edges... and worst of all... the recoil that you will endure from contacting live AC can and will do more damage to you than contacting the voltage itself. Literally.... people have been thrown far distances. Respect any voltage source and you'll be fine. Also, make it mandatory that someone in your theater know CPR and that they are aware that you are working on AC/DC equipment.

Above all SAFETY FIRST around ANY electricity!

And check Out These Cool Electrocution Photos!

And I used to work around an 18kv 20 amp source!

Mark

Posted by Charles Greenlee (Member # 3856) on 07-13-2006, 11:03 PM:

Mark, I love it. Blah blah blah, safety first. And I agree with you, but I love the wrap up, it like "Oh by the way, check out these really cool electrocution pics" Smooth. [Cool]

Posted by Frank Dubrois (Member # 3042) on 07-14-2006, 12:03 AM:

Mark,

you said that you can also get better diodes fairly cheap. I think we spend about $30-$35 for the crap christie diodes. What are the "good" ones going for? and whats the source?

Posted by Gordon McLeod (Member # 33) on 07-14-2006, 03:24 AM:

You know Mark I only replace the bad diode and most of those rectifiers spend another 10 years before they have an issue
the one exception is the allinson rectifiers as they are matched sets

Posted by Frank Angel (Member # 248) on 07-14-2006, 07:06 AM:

DAMN that Photoshop! Yah, very cool pics, but fortunately for the guy on the pole, there's a 90% chance this is just very pretty doctoring. How to tell? Check out his partner in the lift (with the hard hat). What to you think the chances are that he would still be in the same postion in picture 3 that he is in picture 1? His buddy explodes above him and after all those spectacular fireworks, he is still reading or whatever he is doing in picture 1. VERY suspect.

On the other hand, it sure does make for a dramatic reminder when playing around electricity.

BTW, even before you insist that someone in close proximity know CPR, never ever work around electricity alone, especially after hours like many of us do after the theatre closes.

Posted by Mark Gulbrandsen (Member # 72) on 07-14-2006, 07:48 AM:

quote: Frank Dubrois
I think we spend about $30-$35 for the crap christie diodes.

Clearly Frank... if this is for a diode in a 2kw unit you are getting ripped off...! We might charge that for cetain 4K diodes but I don't think so. No, I won't divulge where we get the Semikron diodes from and we do get them in quantity.... You have to learn to do some of that figuring out on your own. There is a google and an internet out there to utulize. Even the IR diodes can be bought for very little $$ each but they are almost the same price as the higher rated Semikron is..

quote: Frank Angel
What to you think the chances are that he would still be in the same postion in picture 3 that he is in picture 1?

Frank,

Note that the guy in the bucket's head is above the roof line in photo # 1, at the roof line in #2, and below the roof line in photo #3. Also note the flexing wire the guy is getting fed the 16kv from being in different positions. I bet that whole thing lasted less than 3 seconds and while the bucket guy was on his way down. Power companies train their guys to look in the direction they are headed in those lifts for good safety reasons. Most Nikon or Canon motor driven cameras are capable of 6 fps.

Gord,

Humm, I know a guy in Kinmount that needed diodes replaced sooner than 10 years. But what the heck... there is nothing wrong with getting in an extra service call or two....

Mark

Posted by John Pytlak (Member # 331) on 07-14-2006, 09:25 AM:

I suspect the photos of the guy "frying" are the real thing. The article says he survived. How? Even if the current going though his body didn't stop his heart, wouldn't vital organs have been "cooked"? I imagine he suffered severe electrical burns over most of his body.

I agree that it is just too dangerous to work on energized power circuits, especially in close quarters like the inside of a rectifier. One slip of the meter/scope lead may shock or startle you into making fatal contact, or throw you across the room. And even if you disconnect the power, don't forget to discharge any capacitors -- the bleeding resistor intended to discharge them may have failed, and you don't want to be "shocked" finding out. [Eek!]

Posted by Randy Stankey (Member # 64) on 07-14-2006, 10:32 AM:

quote: Frank Angel
never ever work around electricity alone, especially after hours like many of us do after the theatre closes.

Most places I work or have worked don't have lockouts on the electical service panels. Instead, when I work on electrical equipment, I shut off all the breakers in question then put a piece of gaffer's tape (duct tape) over the service panel door, sealing it shut.

A good strip of 2" wide Permacel will make a racket as it's peeled off the thin, metal door. If I hear that sound, I can go holler at the idiot trying to fool around inside the panel.

I usually do this even if I'm alone in the area. It only takes 10 seconds to do it.

Posted by Brad Miller (Member # 2) on 07-14-2006, 11:19 AM:

quote: Mark Gulbrandsen
No, I won't divulge where we get the Semikron diodes from and we do get them in quantity.... You have to learn to do some of that figuring out on your own.

Well now that's a bit rude. You come on here and tell everyone that the diodes you use are better than everyone else's and then refuse to divulge the source? So much for spreading the knowledge and improving presentations worldwide I guess.

Posted by Richard Fowler (Member # 893) on 07-14-2006, 12:44 PM:

I generally sell IR 72HFR600 diodes ( instead of the wimpy 42 amp as used in IREM ) for $18.50 SEMIKRON a little more [Smile]

Summer and Christmas peak purchase time with 100's out the door [Cool]

Posted by Mark Gulbrandsen (Member # 72) on 07-14-2006, 01:06 PM:

quote: Brad Miller
You come on here and tell everyone that the diodes you use are better than everyone else's and then refuse to divulge the source?

Exactly... Frank is a consumer and out of respect for other dealers that are on this site I won't be the one to tell all except that there is a better diode. Frank is more than capable of figuring it out by doing some very easy studying on each manufacturers web site.

If you send me an e-mail I'd be happy to share it with you since you are a legitamate dealer and its your site so if you in turn want to post it here you can. I just respect other dealers trying to make an honest buck too! I think Richards pricing is more in line with what an 85 amp diode might cost from the average dealer, since we buy large quantities we are somewhat lower than that.. passing some savings on to the customer. The nice thing about the Semikrons aside fomr the double current rating is that they are available with braided lead attached as is used in IREMS or without the leads.

John,

I think that guy survived because he was elevated above earth ground, the phone pole being a poor conductor well above earth ground... literally... had he been standing on the ground he would have been burnt to a crisp in seconds. I'm sure that his body has never been the same again. I would also assume alot of brain damage also occured.

Mark

Posted by Richard Fowler (Member # 893) on 07-14-2006, 01:31 PM:

Pricing for competitive purposes [Smile]

response expected [Big Grin]

Diode War.....not [Cool]

Posted by Brad Miller (Member # 2) on 07-14-2006, 02:14 PM:

I've got a stack of diodes on the shelf. Perhaps when the day comes that I actually USE some of them, I'll hit you up for that. In the meantime, it has quite literally been about 4 years since I've had any diode failures (all were in Strong consoles big surprise) and before that it was circa 1992 on CFS consoles. I have honestly NEVER had a diode failure in a Christie, IREM, or anything else.

Maybe I'm lucky...or maybe the equipment likes me better. [Big Grin]

Posted by Tim Reed (Member # 137) on 07-14-2006, 02:21 PM:

quote:
A REAL ELECTROCUTION .... this guy survived the contact with the high voltage...

If he survived, then he wasn't electrocuted. [Razz]

(Deja vu. We've had these pix on here before, and I think I said the same thing then.)

Posted by Louis Bornwasser (Member # 3063) on 07-14-2006, 02:47 PM:

Right, Tim; just like the 6 o'clock news: an electrocution implies death; not recovery. Louis

Posted by Mark Gulbrandsen (Member # 72) on 07-14-2006, 05:06 PM:

Brad,
Give em enoughh time and thermal cycles and they will fail. We service a ton of locations in 14 states with all sorts and ages of recifiers with some Christie rectifiers that are 40 years old. We have SLC Consoles that are 10 plus years old. We've also seen alot of rectifier cooling fans in the fail... very dusty out here.

Buildings that have surge protection have less trouble but still eventually experience thermal and then mechanical failures. Most of the IR diodes are epoxy passivated(sealed)and the epoxy is part of the problem eventually letting go at the seal(stem to epoxy). Glass passivated diodes... like Mil-Spec are alot less prone to thermal failures because th glass does not break down over time like the epoxy does.

Mark

Posted by Michael Schaffer (Member # 1204) on 07-14-2006, 05:14 PM:

quote: Mark Gulbrandsen
Exactly... Frank is a consumer and out of respect for other dealers that are on this site I won't be the one to tell all except that there is a better diode.

Huh? You tell us all the time that there are better processors (namely Panastereo) than the ones most dealers want to sell us, so where is the difference?

Posted by Mark Gulbrandsen (Member # 72) on 07-14-2006, 07:02 PM:

Humm, It should be obvious I think to most. The difference is that I told you the name of the better processor(that was common knowledge among many technicians back then anyway) but I didn't tell you the part number of the better diode. There is no reason that Frank can't investigate this for himself unless of course you think he is too lazy or some other reason... I don't think he is lazy since he wouldn't be attempting to repair his own equipment.... and he will learn something important about being a technician in the process.

Mark

Posted by Frank Dubrois (Member # 3042) on 07-14-2006, 07:23 PM:

Mark,

I hope I havent done something to offend you in the past, but the last couple replies from you havent been exactly cordial. I've always respected your opinion here, but am puzzled at your recent "snob like" replies. I appreciate you letting me know there are better diodes out there, and I would like to get those for our projector, so I didnt see the harm in asking your source. I never expected to get them for wholesale or go into business reselling them, just another place to purchase them. I knew we were getting ripped off on the bearings we were getting, so I found a new place to get them much cheaper. I felt we were probably getting ripped off on our diodes as well..now I KNOW we are. I just wanted to save our theatre some money, not corner the market on diodes.

Posted by Michael Schaffer (Member # 1204) on 07-14-2006, 07:41 PM:

Frank - nothing personal. Mark is always like that [Big Grin]

Must have something to do with living in Utah, surrounded by so many funny people. Sooner or later, that gets to you [Wink]

Posted by Frank Dubrois (Member # 3042) on 07-14-2006, 07:44 PM:

oh..Utah [sleep]

Posted by Michael Schaffer (Member # 1204) on 07-14-2006, 08:11 PM:

RE the pictures, if they are indeed authentic:

"This person who is high on PCP was trying to kill himself.
...
Reached out his hand and grabbed the conductor! At that instant 16,600 volts shot through his body.
...
If you can believe it , this guy survived the contact with the high voltage and to this day is still alive! If you made it to this point-- YOU GOT GUTS!!!"

I would rather say - If you made it so this point -- YOU ARE AN IDIOT!!!

Since he allegedly surived, he didn't even qualify for a Darwin Award nomination.

Posted by Frank Dubrois (Member # 3042) on 07-14-2006, 09:23 PM:

In the "electrocuted" picture, the flame kind of seems like it takes on the shape of a person. When I first saw it, it reminded of that scooby doo episode with the 10,000 volt electricity monster. Looks like him.

Posted by Mark Gulbrandsen (Member # 72) on 07-14-2006, 11:39 PM:

quote: Michael Schaffer
Mark is always like that

Great Hornytoads... I love gett'n you guys all farred up... it gets you postin here! [Smile]

Mark

Posted by Michael Schaffer (Member # 1204) on 07-15-2006, 12:43 AM:

Mark - I was defending you. Please don't destroy that.

Posted by Charles Greenlee (Member # 3856) on 07-15-2006, 03:44 AM:

Power supplies, and componets lifespans can differ creatly depending on how clean the incomeing power is. Downtown here, there is alot of noise in the power, whether it be from poor handling equipment, or outside RF or whatever, it is very noisy. Not to mention it's easy to lose power, frequently and in breif flashes. This means your power supply is having to work harder to produce the smoooth DC power your equipment needs. My friend had to replace his power supply on his coumputer a few times before he bought a power conditioning ups. Surges are the main culprit, even if they don't "blow" something, they can weaken it without any symptoms, and after a period of several times, it simply fails. There are also the opposite of surges, which surge protectors don't compensate for, of which the extended version would be a brown out. Those can also be devistating. Here, my power is pretty clean, almost a perfect 60Hz Sine wave, and few surges. So I could probably run for a long time simply plugged straight into the wall.

My point? That is, if you haven't had to replace your diodes in 10 years, it's most likely you live in an area that has good power. That is good. Be glad. If you're like the local Wynnsong, and power can fluctuate every time a red car drives by, or a bird flaps its wings, you'll be replacing your diodes more often. Also it depends on what's putting the load on the diodes, if your equipment is putting a higher load than they can handle (even if they're rated for that load, they can simply be weak). Or say they're rated for 20 Amps, your system runs at 15 Amps, you're fine. But you forget when the lamp initially fires it momentarily, in less than a blink of an eye, spikes up to 30 amps, which you don't ever notice. 1 spike won't kill a diode, nor will 10 or maybe 100, but 1,000 shows later the diode is just worn out. Not assuming these numbers are real, just expressing a logic. And I sure wish I didn't have to replace any diodes, I had to do it 3 times at the Wynnsong, but they weren't on the same projector.

Posted by Louis Bornwasser (Member # 3063) on 07-15-2006, 09:39 AM:

One of my customers (IREM rectifiers) had multiple diode failure as well as phone, computer, game and light bulb failure. Turns out that the power company high voltage guy had wired EVERY pole wrong for 15 years in this community. The locals accepted it as normal.

Before sueing the electrical engineer, our customer gave him one more chance; he brought in his University professor who noted that the power tranformers on the pole were incorrectly connected. (high voltage ground). Every transformer bank in the county was checked and more than 100 were corrected. Problem solved.

Sometimes it IS the power company! Louis

Posted by Richard Fowler (Member # 893) on 07-15-2006, 01:05 PM:

Back to the price on the diode I generally supply for IREM; it does include a welded insulated lead. I supply the same diode for much less without the lead but I find field installs with screw on or poorly soldered leads end with premature failure. I am selling to markets with dirty power, low or large daily voltage swings. The most trouble free regarding diodes has been Kneisley rectifiers;changing capacitors due to age but in the last 28 years possibly 3 - 4 diodes.

Posted by Frank Dubrois (Member # 3042) on 07-15-2006, 09:15 PM:

OK, let me ask this. What SHOULD we be paying for diodes?

Posted by Mark Gulbrandsen (Member # 72) on 07-17-2006, 06:31 AM:

quote: Brad Miller
I have honestly NEVER had a diode failure in a Christie, IREM, or anything else.

Brad,

Give em time... we have some of the first SLC's made, I think they are 11 years old now. Also, lots of 4kw Irem's thata re also becomming very aged.... in fact it was the Irem's that use the Semikron diodes... that led me to find the same diode without the leads attached in both forword and reverse configurations.

quote: Frank Dubrois
OK, let me ask this. What SHOULD we be paying for diodes?

Again, THATS something you have to discover for yourself... try calling 3 or 4 different dealers and see who gives you the best price.... as loong as its a quality diode get them from the least expensive source.

Mark

Posted by Richard Fowler (Member # 893) on 07-17-2006, 08:46 AM:

Ahhhh...Mark is such a diode teaser [Big Grin]